The present invention relates generally to prosthetic devices for middle ear reconstructive surgery. More particularly, the present invention is directed to ossicular prosthetic devices for replacement of the middle ear auditory ossicles.
The human ear is an extremely complex and intricate organ which, through a variety of processes, not all of which are presently understood, provides the valuable sense of hearing. As will be well appreciated by those skilled in the art, the structure of the human ear is typically divided into external, middle, and inner ear portions. The external ear comprises that portion which encompasses the auricle as well as the auditory or ear canal which terminates in the tympanic membrane or ear drum. The middle ear is concerned primarily with the transformation of acoustic energy into mechanical energy, whereas the inner ear is concerned with the transduction of mechanical energy into neural impulses. The middle ear is a rather irregular air filled space in the petrous portion of the temporal bone. The three small bones, or ossicles of the middle ear are the malleus, the incus, and the stapes, which provide mechanical linkage between the tympanic membrane and the fenestra vestibuli. The fenestra vestibuli is an opening in the vestibule of the inner ear and it is commonly referred to as the oval window. The malleus includes a handle which is normally attached to the tympanic membrane, and the stapes includes a footplate which is normally secured in the oval window membrane.
Middle ear air pressure is equalized by the eustachian tube which connects the middle ear and the nasopharynx. This pressure equalization is necessary for normal ear drum movement, and failure of pressure equalization reduces auditory acuity by inhibiting ear drum and ossicular motion.
The most important function of the middle ear is to amplify and deliver sound vibrations from the ear drum to the inner ear, and the second most important function is to protect the inner ear from very loud sounds and physical trauma. Lever action of the ossicles appears to produce greater forces at the oval window than developed at the ear drum, and significant sound amplification occurs. When the ossicular chain is disrupted as by traumatic injury, infection, disease or the like, the reduction in transmitted pressure results in the loss of hearing.
Successful ossicular chain repair and/or reconstruction remains a major challenge for the practicing otologic surgeon. As will herein be described, a variety of prior art prosthetic devices have previously been proposed for replacement of various of the middle ear sound conducting ossicles. Suitable prosthetic devices may be comprised of a variety materials which have been suggested in the literature, some involving the use of autologous and homologous tragal cartilage, plastic materials such as polytetrafluoroethylene (TEFLON), and other plastic materials sold under the trade names Proplast and Plasti-Pore. Other prior art developments have encouraged the use of various inert metallic materials such as platinum, stainless steel and the like. However, a recent histological evaluation of tissue response to plastic materials appears to demonstrate adverse responses.
A recent experiment has revealed that the use of the aforedescribed plastic materials may result in the development of unwanted mucosa within the tympanic cavity, and multinucleated giant cells and macrophages may predominate in the porosity of plastic implants. For a detailed explanation of the foregoing, reference is directed to an article entitled Tissue Response to Plasti-pore and Proplast Otologic Implants in the Middle Ears of Cats, published in the American Journal of Otology, Volume 5, October 1983.
It would thus appear then that the use of neutral or chemically and physiologically inert metallic substances is physiologically advantageous. Moreover, notwithstanding the prior art developments in prosthetic devices, it is desirable to provide a system for total middle ear ossicular replacement.
A variety of prior art patents exist which are directed to prosthetic devices for partial middle ear ossicular replacement. For example U.S. Pat. No. 4,281,419 depicts a ball and socket structure from which a rigid, outwardly extending metallic shaft originates. The latter reference contemplates the surgical dimensioning of the shaft portion and termination of it with biocompatible material in contact with at least a portion of the existing middle ear ossicles.
U.S. Pats. No. 4,473,909 and 4,287,616 disclose auditory ossicular prosthetic devices essentially comprising a flat, plate-like end from which an elongated, generally rigid shaft projects. In both of the latter references the shaft is adapted to be fitted to the remaining ossicular structure of the damaged ear, requiring time consuming precision surgical adjustments and handling by the otologic surgeon.
Another prosthesis for partial ossicular replacement is illustrated in U.S. Pat. No. 3,196,462. The stapedial prosthesis therein disclosed in useful where only the stapes has sustained damaged. The latter reference discloses a generally tubular, barrel-like base adapted to be secured by the surgeon and an elongated rigid stem which extends towards a fat graft adapted to be employed in contact with the oval window.
U.S. Pat. No. 4,215,438 discloses a rigid, generally goblet-shaped prosthetic member preferably formed of stainless steel. The latter device includes a cup portion adapted to receive the capitulum of the stapes, and an integral stem portion which is adapted to be received through a hole drilled into the body of the incus. Another prosthetic device shown in U.S. Pat. No. 4,130,905 includes structure for attachment to the bridge of the human ear and an inwardly projecting stem adapted to contact the stapes.
Russian Pat. No. 584,860 discloses a convex plate terminating in an elongated, elastic tube adapted to be coupled to a portion of the existing ossicles. Russian Pat. No. 619,812 discloses an anvil ossicle prosthesis made from a titanium plate including two parallel leg pieces fixed together by an integral, perpendicular cross piece. The latter device ostensibly increases the effectiveness of sound transmissions through the middle ear. Russian Pat. No. 787,021 discloses an artificial ear bone prosthetic device comprised of plastic material including a generally cross-shaped head from which a slotted shaft projects. A cylindrical sleeve is positioned at a desired portion of the shaft to adapt the prosthetic device for the middle ear of the patient.